(a) Field of the Invention
The present invention relates to an EGR (Exhaust Gas Recirculation) valve device for an internal combustion engine of an automobile, which device being arranged so that a main shaft of a motor is operatively coupled to the valve member which is normally urged to close the valve, and that by applying to this motor an actuating signal obtained through computation on the basis of the amount of the fuel and also the amount of the air which are to be supplied to the engine and further on the informations delivered from various sensors, the degree of opening of the valve is controlled.
(b) Description of the Prior Art
The conventionally used EGR valve device is operated by the manifold vacuum of an engine, and a diaphragm has been employed to form its basic structure.
As such, in the conventional EGR valve device, its operation is influenced by the changes in the negative pressure which are caused due to the wear and degradation of the functions of the respective parts and sections of the engine, and accordingly it has been difficult to accomplish a proper and adequate control of the exhaust gas recirculation. Also, in case it is intended to increase the degree of opening of the conventional EGR valve, this has been entailed by a lowering of the negative pressure, while conversely in case a small degree of opening of the conventional EGR valve is required, this has been followed by an undesirable elevation of the negative pressure. As pointed out above exemplarily, it has been difficult to make an adequate control of the amount of the exhaust gas which is to be recirculated. In order to solve the above-mentioned problem, there has been proposed in the past an EGR valve device having the system such that the EGR valve is of the motor-driven type and that an actuating signal which is obtained through computation on the basis of the amount of the fuel supply and the amount of the air supply and also on the informations delivered from various sensors is applied to the driving motor, to thereby control the degree of opening of the valve (for example, Japanese Patent Preliminary Publication No. Sho. 57-193751). The valve device of the prior art having the above-mentioned system, however, has the following problems that, owing to the arrangement of the device that the main shaft of the motor and the valve rod of the EGR valve are screwed to each other in the "male and female screw" relationship, causing the valve rod to make forward and backward movements by the rotation of the motor, the device as a whole inevitably has tended to have an increased length in the direction of the valve rod, making it difficult to construct the device in a compact size, and further that, because a relatively large motor torque is required, the motor per se inevitably has tended to have a large size also. In addition, in case of a trouble of the motor, this is accompanied by the problem that the EGR valve is left in its open position, thus inducing the engine to plunge into a disorder.